Poor return of hatchery fingerlings in Mississippi state lakes
Mississippi can rightfully boast some of the best crappie fishing in the country in its larger reservoirs and river oxbow lakes, but sustaining good crappie fisheries in small and mid-size impoundments is difficult. Some fisheries managers would say, “not possible.”
Crappie are notorious for wide fluctuations in year-class strength, the numbers of individuals spawned in a given year that remain in the population in the fall or the succeeding year. Crappie fishing can be excellent several years after a strong year class, as crappie grow to 8, 10 and 12 inches. But the good fishing commonly is punctuated by poor fishing following weak year classes.
An obvious solution seems to be stocking crappie to keep recruitment high. A recent study by Mississippi State fisheries researchers Bryant Haley and Wesley Neal evaluated the success of crappie stocking in four of Mississippi’s 20 state fishing lakes.
Hatchery-produced fingerling white crappie were stocked into the four lakes ranging in size from 70 to 180 acres at 50 fish per acre in 2015. Magnolia crappie — a hybrid between white crappie and black-stripe black crappie — were stocked at the same density in 2016. All fish were marked with dyes that allowed detection of stocked fish by microscopic examination of the otoliths (ear bones).
Fingerling white crappie were also stocked into newly renovated Lake Monroe, assumed to lack crappie, to serve as a reference lake and to monitor marking effectiveness.
Crappie populations were sampled immediately before stocking in 2015 and 2016 and in the summer of 2017.
The wild-spawned, age-0 crappie averaged 5.1- to 5.4-inches long when the hatchery-produced crappie were stocked. The hatchery crappie were 2.8- to 3.1-inches long when stocked.
Only 11 hatchery-produced crappie were collected among all lakes and all sampling years. Ten of those fish were collected in previously crappie-free Lake Monroe.
Some success has been achieved stocking crappie. Stocked crappie made an 18 to 74 percent contribution to crappie populations in large (3,000 to 30,300 acres) reservoirs in Tennessee. However, stocked crappie were less than five percent of the crappie population in Lake Chicot, Ark., a 21-mile-long oxbow lake now isolated from the Mississippi River, after several years of stocking. The low return observed in Mississippi’s state lakes matches the consistently low returns from crappie stockings in small to mid-size (140 to 1,240 acres) lakes in Arkansas, Florida, and Tennessee.
Lake size may have something to do with the effect of stocking crappie. Haley and Neal found a positive relationship between lake size and percent contribution of stocked crappie when they analyzed the pooled results from their and other studies.
This relationship — better survival of stocked crappie in larger lakes — may be attributed to largemouth bass predation. Young crappie occupy the open-water zone of lakes; bass forage primarily in the shallow, shoreline zone. In smaller systems, where the shoreline zone is a larger proportion of the total habitat than in larger lakes, the crappie are exposed to greater predation by the bass.
Smaller lakes with high proportions of shoreline-zone habitat also have higher densities of largemouth bass, further increasing bass predation on the crappie.
The poor success may also be partly attributed to the smaller size of the stocked crappie compared to the wild-spawned crappie. The smaller size would make them more vulnerable to bass predation. It would also make them less able to successfully compete with their larger, wild-spawned siblings.
Stocking larger fingerlings and releasing the fish into the open-water zone rather than at boat ramps may improve the survival. Ongoing research at Mississippi State is exploring off-season crappie spawning, an approach that could be used to produce fingerlings earlier in the year, thus, equivalent to the size of the wild-spawned crappie at the time of stocking.
Studies on other fish species have found improved survival when naive hatchery-reared fish have been exposed to natural habitats and predation prior to stocking. This approach, possibly achieved by first releasing the crappie into predator-free exclosures installed in the lake, may also benefit crappie survival.
While some questions await answers, the present knowledge indicates stocking crappie to supplement existing populations in smaller impoundments is a waste of limited fisheries resources. But even if post-stocking survival was increased, a significant dilemma remains: managers don’t know the strength of a crappie year class until late summer or fall when it is far too late to initiate hatchery production of crappie fingerlings.